The present invention relates to an antenna assembly suitable for wireless transmission of analog and/or digital data, and more particularly to a parasitic element antenna assembly for single or multiple band wireless communications devices.
There exists a need for an improved antenna assembly that provides a single and/or dual band response and which can be readily incorporated into a small wireless communications device (WCD). Size restrictions continue to be imposed on the radio components used in products such as portable telephones, personal digital assistants, pagers, etc. For wireless communications devices requiring a dual band response the problem is further complicated. Positioning the antenna assembly within the WCD remains critical to the overall appearance and performance of the device.
Known antenna assemblies for wireless communication devices include:
1. External single or multi band wire dipole:
Features of this antenna includes an external half wave antenna operating over one or more frequency range; a typical gain of +2 dBi; negligible front-to-back ratio; and minimal specific absorption rate (SAR) reduction (SAR 2.7 mw/g typ @ 0.5 watt transmit power level). Multiple band operation is possible with this antenna by including LC (inductor and capacitor) traps used to achieve multi band resonances.
2. External single or multi band asymmetric wire dipole:
Features of this antenna include an external quarter wave antenna operating over one or more frequency range; typical gain of +2 dBi; and minimal front-to-back ratio and SAR reduction. LC traps may also be used to achieve multi-band resonance.
3. Internal single or multi band asymmetric dipole:
Features of this antenna include a quarter wave resonant conductor traces, which may be located on a planar printed circuit board; typical gain of +1-2 dBi; slight front-to-back ratio and reduced SAR (2.1 mw/g.). This antenna may include one or more feedpoints for multiple band operation. A second conductor may be necessary for additional band resonance.
4. Internal or single multi band PIFA (planar inverted F antenna):
Features of this antenna include a single or multiple resonant planar conductor; typical gain of +1.5 dBi; and front-to-back ratio and SAR values being a function of frequency. A dual band PIFA antenna for 824-894/1850-1990 MHz operation may exhibit 2 dB gain and present minimal front-to-back ratio and reduced SAR of 2 mw/g in the lower frequency band.
A compact single or multiple band antenna assembly for wireless communications devices is described. One multi-band implementation includes a high frequency portion and a low frequency portion, both fed at a common point by a single feedline. Both portions may be formed as a single stamped metal part or metallized plastic part. The overall size is suitable for integration within a wireless device such as a cellphone.
Further, the low frequency portion consists of two resonant sections which are stagger tuned to achieve a wide resonant bandwidth, thus allowing greater tolerance for manufacturing variations and temperature than a single resonant section. This feature is useful for single band antennas as well as multi-band antennas. This feature may also be used to enhance bandwidth for both sections of a dual band antenna as well.
The resonant sections for single or multi-band antennas operate in conjunction with a second planar conductor, which may be provided by the ground trace portion of the printed wiring board of a wireless communications device. An antenna assembly so formed provides a moderate front-to-back ratio of 3-12 dB and forward gain of +1 to +5 dBi. The front to back ratio reduces the near field toward the user of a hand held wireless communications device, thus reducing SAR (specific absorption rate) of RF energy by the body during transmit. Antenna pattern beamwidth and bandwidth is increased for a handset during normal user operation, as compared to a half wave dipole. An antenna assembly according to the present invention may provide increased beamwidth when the WCD is near the user head in the talk position, by a factor of 1.5-2.
An object of the present invention is thus to satisfy the current trends which demand a reduction in size, weight, and cost for wireless communication devices.
Another object of the present invention-is the provision of multiple stagger-tuned resonant elements to enhance operational beamwidth and bandwidth, and providing an improved margin for manufacturing tolerances and environmental effects. An improved beamwidth and bandwidth of the handset may translate into improved communication by increasing the number of illuminated cell sites during operation.
Another object of the present invention is the provision of an antenna assembly which is extremely compact in size relative to existing antenna assemblies. The antenna assembly may be incorporated internally within a wireless handset. A unique feed system without matching components is employed to couple the antenna to the RF port of the wireless handset. The antenna assembly requires small-area RF ground lands for mounting, and is effectively a surface mount device (SMD). Beneficially, the antenna assembly may be handled and soldered like any other SMD electronic component. Because the antenna is small, the danger of damage is prevented as there are no external projections out of the WCD""s housing. Additionally, portions of the antenna assembly may be disposed away from the printed wiring board and components thereof, allowing components to be disposed between the antenna assembly and the printed wiring board (PWB).
Another object of the present invention is an antenna assembly providing substantially improved electrical performance versus volume ratio, and electrical performance versus cost as compared to known antenna assemblies. Gain of the antenna assembly according to the present invention may be nominally equal to an external xc2xc wave wire antenna, with SAR level less than 1.6 mw/g achieved at 0.5 watt input for an internally mounted antenna. The 3 dB beamwidths are significantly higher than a dipole antenna during normal user operation. The performance characteristics are found across a wide range of environmental operating conditions, e.g., at temperatures ranging from xe2x88x9240 to +60 degrees C.
Components of the antenna assembly may be manufactured in different ways. It is conceivable for example that the antenna can be formed from a punched or etched sheet. In a preferred embodiment, the antenna may be formed from a single-piece metal stamping adaptable to high volume production. Additionally, capacitor elements may be coupled to the antenna assembly through known high volume production techniques.
Another object of the present invention is to provide an antenna assembly having improved operational characteristics, including an increased front-to-back ratio and a decreased specific absorption rate of RF energy to the user of an associated wireless communications device.
Accordingly, it is the primary object of the present invention to provide an improved antenna assembly for communications devices including portable cellular telephones and PCS devices with improved directionality, broadband input impedance and increased signal strength. The present invention additionally reduces radio frequency radiation incident to the user""s body and reduces the physical size requirements for a directional antenna assembly used on communications devices.
It is still an additional object of the present invention to provide a compact antenna assembly suitable for incorporation within the housing of a portable wireless communication device. The current invention provides compact, discrete antenna assembly without external appendages, such as provided by known external dipole antennas.